The crossword presented here is a crossword variant type known as "Going Too Far", which was invented by Mike Shenk. Many of the answers (but not all of them) extend into the shaded squares in the grid, with each shaded square receiving exactly one letter as a result. The letters in these squares, when read from left to right and top to bottom, spell LET NINE OVERLONG ANSWERS GO A STEP FURTHER PER THE SONG'S SUBTITLE.
The song in question is "Single Ladies" by Beyonce (as referred to in 26 and 76 across), and the subtitle referred to is "(Put a Ring on It)". Nine answers can be extended an extra square by putting an O in an adjacent square over which forms a new word, and simultaneously acts as a circle in that square. (The new words formed in this way are CELLO, OINKED, ORATION, STENO, OASIS, DINERO, LASSO, OBLAST, and RODEO.) Reading the letters circled in this way from left to right spells out the answer to this puzzle, TRAPEZIUS.
A completed solution grid for the puzzle has been provided for reference.